The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent that it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Exhaust brakes may be used for vehicle braking in diesel engines. When an exhaust brake is activated, an exhaust path downstream of an engine is closed or reduced to cause the exhaust gas to be compressed in the exhaust manifold to generate back pressure. With the increased back pressure in the exhaust manifold, load on the engine is increased, thereby slowing down the vehicle. The back pressure in the exhaust manifold and consequently the braking torque applied to the engine are generally proportional to an engine speed.
A variable geometry turbocharger (VGT) may regulate exhaust gas flow that passes through the VGT to control the back pressure in the exhaust manifold. Vanes of the VGT are generally set at a fixed position to accommodate a situation where the engine runs at a maximum speed. At the maximum engine speed, a maximum braking force is required for effective engine braking and the exhaust flow through the VGT is also at its maximum. The fixed flow passage defined by the VGT is larger than necessary to generate a desired back pressure at low engine speeds. As a result, the exhaust brake is less effective at lower engine speeds.